Low RPM stumble

I was going to hook it up to the vacuum port on the carb.

And I took a look at the carb, the secondary float level seems good, but the primary one seems low. When I took the sight plug out of the primary one, no fuel came out, and I could barely see any in there, and when I opened the secondary sight I could see a slight trickle come out. Could this be the issue? Under cruise when it's only using the primary it runs out of fuel, and when I get on it and the secondaries are used it gets enough fuel to run better? Because a lean condition would cause popping right?